Problem: William is 16 years older than Ashley. Sixteen years ago, William was 5 times as old as Ashley. How old is Ashley now?
Solution: We can use the given information to write down two equations that describe the ages of William and Ashley. Let William's current age be $w$ and Ashley's current age be $a$ The information in the first sentence can be expressed in the following equation: $w = a + 16$ Sixteen years ago, William was $w - 16$ years old, and Ashley was $a - 16$ years old. The information in the second sentence can be expressed in the following equation: $w - 16 = 5(a - 16)$ Now we have two independent equations, and we can solve for our two unknowns. Because we are looking for $a$ , it might be easiest to use our first equation for $w$ and substitute it into our second equation. Our first equation is: $w = a + 16$ . Substituting this into our second equation, we get the equation: $(a + 16)$ $-$ $16 = 5(a - 16)$ which combines the information about $a$ from both of our original equations. Simplifying both sides of this equation, we get: $a + 0 = 5 a - 80$ Solving for $a$ , we get: $4 a = 80$ $a = 20$.